This invention relates to an operating device for an electric chain block for changing winding-up and -off operations and controlling raising and lowering speeds.
There have been operating devices for electric chain blocks for the above operation and control. In general, such a hitherto used operating device comprises an operating box which moves independently of movement of a chain or hook. There are provided in the operating box push-buttons for raising and lowering operations and speed control means including a potentiometer and like for determining winding-up and -off speeds in step or stepless manner. An operator actuates the push-buttons and the speed control means to change the raising and lowering operations and control the winding-up and -off speeds in no direct connection with movement of the chain or hook.
Recently, working conditions have been improved. For example, weights of heavy objects to be carried by laborers have been severely limited and a regulation prohibits a laborer from being forced to carry an object heavier than a determined weight. Under such circumstances, an electric chain block has been expected which is simple in construction and easy to operate as if the chain block were hands and feet of a laborer.
In view of simplicity in operation of the chain block, it is preferable for the laborer to operate the chain block in the same sense as he lifts up a heavy object by himself. In order to realize such an ideal electric chain block, it is considered important to construct the electric chain block in a manner such that when it is desired to raise or lower a heavy object, the chain block immediately starts raising and lowering only by raising or lowering an operating box by an operator. Moreover, it is more preferable to control winding-up and -off speeds by raising and lowering distances of the operating box in order to simplify the operation of the electric chain block.
However, with the hitherto used operating devices for the electric chain blocks, the raising and lowering operations are changed and winding-up and -off speeds are controlled with no relation to the movement of the chain or hook as above described. An operator thus operates the electric chain block in a sense quite different from that when he is lifting a heavy object by himself. Therefore, the hitherto used electric chain blocks are lacking in simplicity of operation.